Radio direction finder



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RADIO DIRECTION FINDER Filed Dec. 29, 1942 2 Sheets-Sheet 2 atented Aug. 24, 1948 RADIO DIRECTION ER Alfred R. Starr, New York, N. Y.

Application December 29, 1942, Serial No. 470,522

17 Claims. (Cl. 34a-1123) The invention here disclosed relates to direction nders and the purposes of the invention' broadly are 'to operate on the maximum, instead of on the minimum signal as heretofore, whereinterierence has prevented sharp and accurate readings, and to obtain the proper sense of the bearing. so as to know at once the true direction oi signal origin.

A further object of the invention is to make it possible to obtain closer and more accurate readings than have been heretofore attainable.

Other desirable objects and the novel features by which all purposes of the invention are attained are set forth or will appear in the course oi. the following specification.

The drawing accompanying and forming part o1' the speciilcat'ion illustrates various features t and practical embodiments of the invention. It

is realized however that such features and structure may be modi-ned and changed in various ways all within the true spirit and broad scope of they illustra-ting the in-phase cumulative effect obtained in the direction of the sign-al and the outof-phase blocking or cancelling eect of signal forces in the other lobes oi' the diagram, Fig. 3.

Fig. 6` is a diagrammatic view illustrating a modification.

The apparatus comprises in the ilrst instance. a pair of loop aerials A and B. mounted, preferably in angularly adjustable relation, on a rotatable post or support 1, which may carry an indicator or pointer 8, reading on a direction scale 9.

The respective loops are connected by wiring I and il. with radio frequency amplifiers I2 and I3. identical in respect to gain and selectivity.

The outputs of the R. F. ampliiiers are fed into a series plate combining circuit. which may be similar to the one disclosed in the Alfred R. Starr Canadian lPatent 246.183. In the present illustration, the R. F. ampliiiers are shown coupled by transformers Il. i5, into the plate combining circuit.R. I". amplier A feeding into the grid of tube A, which is biased to the cutoi! point by battery C and ampliiler B feeding into the grid of tube B, similarly biased.

'The plate circuits of the two tubes are connected in series by connection it, from the cathode of tube A tothe plate of tube B.

The combined plate circuit is shown connected at il, into the primary of an input transformer i0, feeding into a conventional audio amplier I9.

The output of audio amplier i9, may be fed into any suitable indicating device, such as a catl1- ode ray tube 20, loud speaker, electron. ray tube, output meter or the like.

The loops are designed with proper inductance to tune to the samefrequency as the following R. F. stages, preferably with the same size condensers and these condensers 2i 22, together with the variable condensers of the R. F. ampliiiers may be al1 mounted on one shaftor otherwise mechanically connected as indicated at 23, 2d, 25.

These tuning controls of the loops and R. F. amplifiers may all be operated from a single dial as by means of pulleys, belts, gears or other connections.

The R. F. amplifiers may be of conventional or special design and the same is true of the audio ampliner.

Volume controls are indicated at 26, 21, for varying the intensity of the signals from the loops and these are indicated mechanically connected at 2d, for operation from a single control knob or the like.

Fig. 3 shows theresponse curves of the two crossed loops superimposed one on the other, loop A producing the aligned; large and small circular lobes a, a' and loop B producing similar lobes b, b'.

The circuit shown in Fig. 1 is designed so that only parts of the response curves which are common will give a signal response. These parts are shaded to show the overlapping portions of the larger lobes a. b. producing an elliptical response lobe ab, and lesser elliptical lobes a'-b, a--b and o o'. The lobe a--b is the resultant output of the series plate circuit when the instantaneous potentials of both loops are positive. The result is a sharp maximum response in the direction of signal origin. The angle between the crossed loops may be varied as by reducing the included angle' between the loops to increase the sharpness of response. The angular relation shown however has proved satisfactory for most purposes.

The properties of t'he circuit are such that the effects of the lobes of. the combined response curves which are not wanted are automatically blocked out and only the effect of the lobe in the sector from which the signal is coming remains.

The ordinary loop direction iinder operates on the minimum signal, where interference may prevent obtaining a sharp and accurate reading, whereas in the present invention a. sharp signal is obtained in the indicating circuit. This maximum signal is less likely to be affected by interference because the signal-to-noise ratio is greater.

Also the present invention gives the proper sense of the bearing, without going through the second operation of switching in a second antenna, such a's has been necessary heretofore.

Thus time is saved by getting the correct reading in one operation.

Reversing switches 30, 3i, Fig. 6, may be interposed in the leads Il) and I l, to change the polarity ci ach loop. Then by means of certain combinations of switching. it is possible to choose the sector from which the loops will receive,'mak ing it only then necessary to turn the loops through an angle of 90 in order to sweep around a complete circle.

The new circuit has some inherent antenna efiect tending to make the circuit unidirectional. the antenna loops being unbalanced as by being grounded at one s ide of the tuning condensers 2|, 22, as at Fig. 6. A vertical antenna 32 may be added or switched' in if desired, to eliminate the smaller lobe substantially entirely.

Due to the directional eiect, this new system will discriminate against radio interferenceV or noise" to a greater extent than the ordinary loop direction finder. v

For instance, the total noise coming from randoin. directions will be approximately in proportion to the active lobe of the combined response curves, whereas in the ordinary loop, the total noise will be in proportion to the full area of the YESIJOIlSE Cill'VC. l

In actual operations only the combined lobe a-b oi Fig. 3 is effective. The lobes a and b' are smaller than lobes ab because of antenna effect. As a consequence, the combined lobe ab' is smaller than the combined lobe ab in the direction of the signal and by reason of the'tubes in the series plate circuit being biased beyond the cutoff point, signals in the region a'b' disappear.

Signals in the region of the lobes a-b' and b-a' also disappear because of the grids of tubes A and B being alternately positive and negative, so that no current will ilow in the common plate circuitl l'n further explanation of the fact that the undesired sections ab' and ba' are automatically blocked out, it may be assumed that the instantaneous polarity of loop A is such that the grid of tube A is positive and that the polarity of loop B is such that the grid of tube B is positive. 'I'hen the plate circuit will be conductive during the positive half cycles as shown on the characteristic curves at a and b, Fig. 4. Therefore, any signal in the sector ab will cause a response in the indicating device.'

Assuming a signal in sector ab', loop aa will be positive and loop bb' will be negative. -The gridof tube A will be positive and the grid of tube B willbe negative at the same instant. During the next half cycle grid of tube A will be negative and grid of tube B positive as represented in Fig. 5. Therefore, no current will :Elow in the plate circuit and any signal in this sector would not register on the indicating device. Similarly, any signal in sector b-a' will be blocked out.

The invention has many uses, for example as a homing device for airplanes, direction nding for airplanesfrom ground stations. location ot enemy planes from 'ground stations by triangulation, marine direction finding, direction ilnding on airplanes from beacons, use with reflected signal systems for altimeters and for determining distance and the like.

The apparatus required is relatively simple and inexpensive for the results attained. 'I'he System may be further simplified by employingl a double grid tube 33, Fig. 6, in place of separate tubes A and. B first shown, connected to accomplish the cumulative maximum signal effect from the two crossed loops.

What is claimed is:

1. In a direction nder, the combination of two crossed loop antennas, a radio frequency amplier for eachl of said .loop antennas, thermionic devices having input circuits connected with said ampliers and output'circuits connected in series relation, said thermionlc devices being severally biased to normally prevent current flow in said output circuits and an indicating device connected with the output circuits of said thermionic devices. A

2. In a radio direction finder, the combination of two crossed loop antennas, a radio frequency amplifier connected with each antenna. two thermionicv devices connected with said amplifiers, said thermionic devices having output circuits connected in seriesrelation. said devices being severally biased to normally prevent current flow in said output circuits, whereby a, sharp maxirnum response is obtained from said loop antennas and indicating means connected with said series connected output circuits.

3. `In a radioy direction finder, the combination of two crossed loop antennas, ampliflying devices connected therewith, two thermlonic devices connected severally with said amplifying devices and having output circuits connected in series relation, said thermionic devices being severally biased to normally prevent current ilow in said series connected output circuits and whereby two of the unwanted lobes in the combined response curves of said loop antennas, perpendicular to the direction ofsignal are cancelled out, leaving a sharp maximumresponse in the'direction of signal.

4. .In a radiodirection finder, twocrossed loop antennas in variable angular relation to one another, dual ampliers connected therewith, thermionic tube means connected with said dual amplifiers and having plate' circuits connected inseries and whereby three offthe unwanted lobes in the combined response curves are cancelled out by the combined eilct of phase relations and prop.

orties of said series connected circuits,

5. In a radio direction-f1nder, two .croosed loop antennas, an amplifier connected to each antenna, thermionic means having tuned input circuits with grids connected to said ampliers and plate circuits connected in series relation and signal indicating means connected with said series plate circuits for obtaining unidirectional signal response through phase discriminating properties of said series output circuits.

l 6. In-a radio direction finder, two crossed loop antennas. amplifying devices connected therewith, a dual grid: vacuum tube having grid circuits connected with said amplifying devices and biased to normally prevent current ow in the plate circuit of said tube, an audio amplifier connected with said plate circuit and signal indicating means connected with said audio arnplmer for sharp maximum unidirectional signal re-V sponse.

7. In a direction finding system, a plurality oi signal intercepting means, amplifying means connected therewith and a signal combining circuit comprising thermionic devices having plate circuits connected in series relation connected with said amplifying means and receptive only to selected desired portions of the response of said plural intercepting means.

8. In a radio direction finder, the combination of two crossed loop antennas, amplifying devices connected therewith and signal responsive devices connected to said amplifying devices and including thermionic devices responsive only to portions of the respective characteristic curves which simultaneously aect said thermionic devices and said thermionic devices having their output circuits connected in series relation and severally biased to normally prevent ow in said output circuits.

9. In a direction nder, two crossed loop antennas, amplifying means connected therewith, an electronic interlocking circuit comprising thermionic devices with their plate circuits connected in series relation for combining the effects of the overlapping portions of two of the lobes of the response curves of said crossed loop antennas to increase the sharpness of the maximum signal response.

10. In a radio direction finding system, a plurality of signal interceptng means and thermionic coincidence devices having plate circuits connected in series relation and receptive only to the common portions of the response of said plural intercepting means.

1l. In a direction finding system, a plurality of signal intercepting means and a signal combining circuit comprising a. plurality oi thermionic devices having plate circuits connected in series relation and receptive only to selected desired portions of the response of said plural in tercepting means.

12. In a radio direction nder, a plurality of signal intercepting means in variable angular relation to one another and a plurality of thermionic devices having respective control grid circuits connected to said plural intercepting means and having plate circuits connected in series relation, whereby the desired common portions only of the response of said plural intercepting means are received.

13. In a direction iinding system, a plurality of signal intercepting means, amplifying meansV connected therewith and electronic interlocking 6 v means comprising thermionic devices having plate circuits connected with said"V amplifying means and operable only by signal forces simultaneously present in said intercepting means.

14. In a direction iinder, two crossed loop antennas, respective amplifying means therefor and an electronic interlocking circuit, comprising a dual grid vacuum tube having negatively biased grid circuits connected with said amplifying means, whereby current is normally prevented from flowing inthe plate circuit of said dual grid tube, and said tube being thereby arranged for selecting and combining only desired portions of the response curves of said crossed loop antennas.

15. In a direction finder, two crossed loop antennas, respective amplifying means therefor and an electronic interlocking combining circuit, comprising a duel grid thermionic device with both grids biased to normally prevent current iiow in the plate circuit, for selecting the sharp maximum lobe and for rejecting other undesired lobes of the combined responsive curves of said crossed loop antennas.

16. In a direction iinder, the combination of crossed loop antennas, amplifying means there for and an electronic interlocking and combining circuit for said amplifying means, comprising thermionic devices having plate circuits connected in series relation and including a phase discriminating circuit for eliminating eifects represented by undesired lobes of the superimposed curves of said crossed loop antennas.

17. In a direction iinder, a plurality of signal intercepting means in angular'relation to ane another, tuned input amplifiers connected therewith, an electronic interlockingandv combining circuit for said amplifiers comprising dual thermionic devices connected in series relation, including a phase discriminating circuit, volume control for said ampliers, means for effecting simultaneous adjustment of said volume controls and means for eiecting simultaneous tuning of said amplifiers.

ALFRED R. STARR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name A Date 1,723,907 Alexanderson Aug. 6. 1929 1,821,650 Kolster Sept. 1, 1931 2,026,254 Sandfort Dec. 31, 1935 

